A. Field of the Invention
This invention pertains to a converter for generating a bit stream representative of a fractional rate encoding which may be incorporated for example into a QAM modem, as well as to a method for the same.
B. Description of the Prior Art
Quadrature amplitude modulation (QAM) has become the standard method of data transmission over long distances because it provides a means of transmitting data at a much higher data rate than the baud rate of a particular channel. However, until now in all the QAM methods used by various QAM modems, because of the inherent limitations of the encoding schemes, the ratio of the data rate and the baud rate of the channel had to be an integer and the number of points in the signal constellation had to be a power of 2, (i.e. 2, 2.sup.2 =4, 2.sup.3 =8 etc.) Improvements in signal transmission methods and circuitry have resulted in significant improvements in the bandwidth of certain channels, but because of the above mentioned constraints, the baud rate of a channel was still limited to values below the actual channel bandwidth.
Schemes for overcoming these problems, involving fractional rate encoding had been tried, but these schemes were limited to a channel having a particular bandwidth and could not be adapted to other channels because of circuit complexity.